Pot-in-Pot earthenware cooling device

Invented in 1995 by Mohammed Bah Abba of Nigeria, the Pot-in-Pot is a ingenious new way to use ancient technology. It consists of two earthenware pots, one slightly smaller than the other, and some sand to go between them. When water is poured into the sand, it evaporates outward into the dry desert air through the outer pot, carrying heat with it. The larger pot has a lip that rests on the smaller pot, so no water can escape from the sand directly into the air. Also, a damp cloth is placed over the smaller pot's opening to keep out sunlight. Thus, even with zero external energy or expensive parts, practical refrigeration has been made possible for Nigerian farmers.

Subsistence farming, by its nature, doesn't leave much room for profit. In the past excess food had to be sold the same day it was harvested, or it would spoil. This job was traditionally done by a Nigerian family's younger daughters, leaving little time for education or play. With refrigeration the family can wait for demand, spending only perhaps one day a week selling produce. The Pot-in-Pot works well enough for eggplants, tomatoes, and peppers to survive more than three weeks, rather than the two or three days that they would keep without cooling.

Besides his brilliance in creating the Pot-in-Pot, Mohammed Bah Abba is also a hero for the way he distributed it to the local farmers. Instead of waiting for demand to come to him, he started a factory with his own money. Each Pot-in-Pot cost about thirty cents to make, so he used his salary as an instructor at Jigawa State Polytechnic to make 12,000 of them. He then gave all of them away between 1997 and 1999 to families in his home state of Jigawa. Right now he's selling them for 40 cents a piece to the states surrounding Jigawa, and has started a few additional Pot-in-Pot factories. By Bah Abba's own estimate in 2000, 75 percent of Jigawa's rural families were using one of his devices.